Conventional liquid crystal display devices are equipped with a lighting device. The lighting device typically includes a light emitting diode for generating light; a first optical element and a second optical element each of which includes one light input surface and one light output surface for shaping light; and an optical axis extending through the light emitting diode, the first optical element, and the second optical element. The light output surface of the first optical element is configured to cause a predetermined light component of the light generated by the light emitting diode to be refracted from the optical axis before entering the second optical element. The light output surface of the second optical element is configured to cause the light component to be further refracted from the optical axis. An example of such lighting device is disclosed in Japanese Translation of PCT International Application Publication No. JP-T-2009-510731.
The lighting device typically includes optical sheets, such as a luminance uniformization sheet. The luminance uniformization sheet includes an optically transmissive base material. On at least one side of the optically transmissive base material, a white diffusion layer is formed by printing in a pattern configured to enable uniformization and output of light having a non-uniform luminance distribution. The portion in which the white diffusion layer is formed has a transmittance such that, when the optical transmittance with respect to the wavelength of 436 nm is one, the optical transmittance with respect to the wavelength of 544 nm and the wavelength of 612 nm is in a range of from 0.8 to 1.6. An example of such optical sheet is disclosed in Japanese Unexamined Patent Application Publication No. 2010-185906.
In the lighting device disclosed in Japanese Translation of PCT International Application Publication No. JP-T-2009-510731, the first optical element and the second optical element are both configured to refract light advantageously in a direction away from the optical axis. In this way, it is made possible to easily expand the region, in the screen to be illuminated by the lighting device, that is illuminated by the light emitting diode used as the light source, even when the distance from the light emitting diode to the screen is set. On the other hand, in the luminance uniformization sheet disclosed in Japanese Unexamined Patent Application Publication No. 2010-185906, the light is diffusely reflected by the white diffusion layer, whereby the input light having a non-uniform luminance distribution can be uniformized and output. The optical reflectance of the white diffusion layer is higher than the optical transmittance thereof. The white diffusion layer, however, may cause a specific tint in the transmitted light or reflected light, depending on the material used. As a result, color unevenness may be caused in the output light of the lighting device.